High-mass star forming regions: An ALMA view Riccardo Cesaroni INAF - Osservatorio Astrofisico di Arcetri

IR-dark (cold) cloud fragmentation (hot) molecular core infall+rotation (proto)star+disk+outflow accretion hypercompact HII region expansion extended HII region Possible evolutionary sequence for high-mass stars turbulence? gravitation? magnetic field?

IR-dark clouds Detected in absorption at 8 µm with ISO, MSX, SPITZER (Perault et al. 1996; Egan et al. 1998, GLIMPSE)  cold and dense Confirmed in sub-mm cont. emission with SCUBA (Feldman et al. 2000) and H 2 CO line (Carey et al. 1998)  2-8 kpc, M O, 1-5 pc, 10 5 cm -3, < 20 K Mapped in NH 3 line with 100-m telescope (Pillai et al. 2006)  K, M O, line FWHM < 3.5 km/s

MSX 8  m SCUBA 850  m Carey et al. (2000) MSX 8  m SCUBA 850  m

IR-dark clouds Detected in absorption at 8 µm with ISO, MSX, SPITZER (Perault et al. 1996; Egan et al. 1998, GLIMPSE)  cold and dense Confirmed in sub-mm cont. emission with SCUBA (Feldman et al. 2000) and H 2 CO line (Carey et al. 1998)  2-8 kpc, M O, 1-5 pc, 10 5 cm -3, < 20 K Mapped in NH 3 line with 100-m telescope (Pillai et al. 2006)  K, M O, line FWHM < 3.5 km/s

NH 3 in IR-dark clouds Pillai et al. (2006)

NH 3 line FWHM and temperature in IR-dark clouds Sridharan et al. (2005) IR-dark clouds IR-dark clouds

Evidence of sub-structure (cores) from PdBI maps of 1mm cont. & CO isotopomers (Rathborn et al. 2005)  M O, embedded stars (outflows) in 30% of cores Evidence of embedded protostars from Spitzer images at 3.6 & 24 µm (Carey et al. 2002)  low- to intermediate-mass stars  IR-dark clouds may be the very first stage of the high-mass star formation process

 Cloud structure: core MF = stellar IMF ?  hint on star formation process: IMF set before or after fragmentation?  Cloud/core velocity field: turbulence (Mc Kee & Tan 2002) or gravitation (Bonnell et al. 2004)?  discriminate between different models ALMA contribution:  will resolve cloud structure & velocity field on all scales from 500 AU to >1 pc  will detect all cold cores up to 20 kpc

Beuther & Schilke (2004) core MF = stellar (Salpeter) IMF dN/dM~M -2.5

 Cloud structure: core MF = stellar IMF ?  hint on star formation process: IMF set before or after fragmentation?  Cloud/core velocity field: turbulence (Mc Kee & Tan 2002) or collapse (Bonnell et al. 2004)?  discriminate between different models ALMA contribution:  will resolve cloud structure & velocity field on all scales from 500 AU to >1 pc  will detect all cold cores up to 20 kpc

Proper motions in Orion (Rodriguez et al. 2006) ALMA can do the same up to 10 kpc! 12 km/s 27 km/s 500 AU

 Cloud structure: core MF = stellar IMF ?  hint on star formation process: IMF set before or after fragmentation?  Cloud/core velocity field: turbulence (Mc Kee & Tan 2002) or gravitation (Bonnell et al. 2004)?  discriminate between different models ALMA contribution:  will resolve cloud structure & velocity field on all scales from 500 AU to >1 pc  will detect cold cores >0.1 M O up to 10 kpc

Numerical simulations of 1-pc clump collapse Bate et al. (2003) ALMA beam 350GHz 10kpc

Continuum spectrum of cold core (sensitivity estimates for 5 hr ON-source) Note: M Jeans ≈ 0.5 M O 3σ ALMA 3σ SMA 3σ PdBI 3σ VLA 3σ ALMA 3σ SMA 3σ PdBI 3σ VLA

Hot molecular cores Typically: 100 K, 10 7 cm -3, >10 4 L O Rich chemistry: evaporation of grain mantles Sometimes with embedded UC HII regions  Believed to be the cradles of OB stars  Association with outflow, infall, and rotation (disks) expected

Cesaroni et al. (1998); Hofner (pers. comm.) UC HII HMC B0.5 B0 B1

Hot molecular cores Typically: 100 K, 10 7 cm -3, >10 4 L O Rich chemistry: evaporation of grain mantles Sometimes with embedded UC HII regions  Believed to be the cradles of OB stars  Associated with outflow, infall, and rotation

Hot molecular cores: outflows High angular resolution needed to resolve multiple outflows, not to image single outflow Requirements: star separation in cluster ≈ 0.05 pc = 0.5”-10” line wings >> 1 km/s line intensity = few K  very easy for ALMA! E.g. 1” resol., 1 hr ON- source, 1 km/s resol.  1σ = 0.1 K  can image any outflow in the Galaxy

Beuther et al. (2002, 2003) IRAM 30m 2 outflows IRAM PdBI: 6 outflows!

Hot molecular cores: outflows High angular resolution needed to resolve multiple outflows, not to image single outflow Requirements: star separation in cluster ≈ 0.05 pc = 0.5”-10” line wings >> 1 km/s line intensity = few K  very easy for ALMA! E.g. 1” resol., 1 hr ON- source, 1 km/s resol.  1σ = 0.1 K  can image any outflow in the Galaxy

Other advantages of ALMA for outflow studies: Measurement of proper motions: 100 km/s at 1 kpc imply 20 mas/yr (at 90 GHz, 1/3 beam ≈ 15 mas)  outflow inclination wrt l.o.s. from V l.o.s. /V p.m.  derivation of deprojected outflow parameters Imaging from 0.01 pc to 1 pc (in different tracers)  possible outflow precession

0.7 pc 200 AU Lebròn et al. (2006) Moscadelli et al. (2005) IRAS ALMA

Hot molecular cores: infall Important to test models for OB star formation, but difficult to detect/recognize: e.g. line broadening towards star may be due to optical depth and/or turbulence Methods & requirements: Red-shifted self-absorption  temperature gradient and thick line(s) [for any star] Red-shifted absorption  optically thick, embedded HII region [only for OB stars]

Absorption line tracing infall in a core with embedded HII region HMC 100 K 10 4 K

Infall velocity field from NH 3 absorption towards HII region Sollins et al. (2005) beam=0.24”=1400 AU maximum redshift towards star G

Red-shifted absorption is a very powerful method to measure infall, but can be used only if: 1.instrumental beam matches HII region diameter  2 R HII = HPBW(ν) = 0.012” [350/ν(GHz)] 2.free-free emission is optically thick   ff (ν) > 1  T B =10 4 K 3.Core opacity is low   dust (ν) < 1  relationships between distance & N Lyman and between frequency & N Lyman

R HII = AU for B0.5-O4 star

Absorption experiment:  HII regions usable to trace infall in absorption: –all HIIs in B0.5 stars (or earlier) up to 1 kpc –all HIIs in O stars up to galactic center (and beyond)  frequencies < 100 GHz preferred: plenty of lines of many molecules!  typical target: hypercompact HII region with  = 1 and R HII = AU Note that HII regions like these are observed!

Hypercompact HII regions from De Pree et al. (1998)

R HII = AU  free-free = B0-O8.5

Hot molecular cores: rotation Conservation of angular momentum  rotation speed up during infall  disk formation Disks in OB stars may solve radiation pressure problem: photon escape along axis reduces radiation pressure accretion focused through disk boosts ram pressure Present situation: a handful of disks (M disk < M star ) seen in early B stars a few rotating toroids (M toroid >>M star ) seen in O stars  Lack of disks in O stars may be observational bias!?  ALMA sensitivity and resolution needed

IRAS Cesaroni et al. Hofner et al. Moscadelli et al. Keplerian rotation: M * =7 M O

Hot molecular cores: rotation Conservation of angular momentum  rotation speed up during infall  disk formation Disks in OB stars may solve radiation pressure problem: photon escape along axis reduces radiation pressure accretion focused through disk boosts ram pressure Present situation: a handful of disks (M disk < M star ) seen in early B stars a few rotating toroids (M toroid >>M star ) seen in O stars  Lack of disks in O stars may be observational bias!?  ALMA sensitivity and resolution needed

Beltran et al. (2004) Beltran et al. (2005) Furuya et al. (2002) hypercompact HII + dust O9.5 (20 M O ) M O Beltran et al. (2006)

Hot molecular cores: rotation Conservation of angular momentum  rotation speed up during infall  disk formation Disks in OB stars may solve radiation pressure problem: photon escape along axis reduces radiation pressure accretion focused through disk boosts ram pressure Present situation: handful of disks (M disk < M star ) seen in early B stars a few rotating toroids (M toroid >>M star ) seen in O stars  Lack of disks in O stars may be observational bias!?  ALMA sensitivity and resolution needed

ALMA PdBI Assumptions: HPBW = R disk /4 FWHM line = V rot (R disk ) M disk  M star same in all disks T B > 20 K obs. freq. = 230 GHz 5 hours ON-source spec. res. = 0.2 km/s S/N = 20 edge-on i = 35°

Assumptions: HPBW = R disk /4 FWHM line = V rot (R disk ) M disk  M star same in all disks T B > 20 K obs. freq. = 230 GHz 5 hours ON-source spec. res. = 0.2 km/s S/N = 20 ALMA PdBI no stars edge-on i = 35°

Hot molecular cores: rotation Conservation of angular momentum  rotation speed up during infall  disk formation Disks in OB stars may solve radiation pressure problem: photon escape along axis reduces radiation pressure accretion focused through disk boosts ram pressure Present situation: handful of disks (M disk < M star ) seen in early B stars a few rotating toroids (M toroid >>M star ) seen in O stars  Lack of disks in O stars may be observational bias!?  ALMA sensitivity and resolution needed!

Summary: ALMA and OB star formation Assess structure of IR-dark clouds in the Galaxy  mass function and 3D velocity of cores prior to star formation Resolve multiple outflows from cluster and measure their (3D) velocity  accurate estimate of outflow parameters Reveal infall in O stars up to galactic center  estimate accretion rates Image circumstellar disks in OB stars up to Galactic center  discriminate between high-mass star formation theories

What ALMA cannot do… Spectrum of deeply embedded OB stars peaks in the far-IR, hence:  precise luminosity estimate impossible with ALMA! High resolution imaging in the sub- mm and mid-IR insufficient (see Orion)  (sub)arcsec resolution at µm!!!  Herschel and FIRI (Far-InfraRed Interferometer) needed

Orion KL 10 5 L O : where from? sub-mm Beuther et al. (2005) NIR-MIR Shuping et al. (2004) FIR ? ALMA

What ALMA cannot do… Spectrum of deeply embedded OB stars peaks in the far-IR, hence:  precise luminosity estimate impossible with ALMA! High resolution imaging in the sub- mm and mid-IR insufficient (see Orion)  (sub)arcsec resolution at µm!!!  Herschel and FIRI (Far-InfraRed Interferometer) needed

HPBW=0.3” obs.freq.=230GHz int.time=5h spec.res.=0.2km/s ALMA

HPBW=0.3” obs.freq.=230GHz int.time=5h spec.res.=0.2km/s PdBI

ALMA can detect all disks (if any…) in O stars up to galactic center! Also important: 8 GHz bandwidth with high spectral resolution  simultaneous imaging of many lines from different species, with different optical depths and different excitation energies  ALMA will make it possible to discriminate between theories of massive star formation (e.g. disk accretion, competitive accretion, etc.)

compact ALMA extended ALMA compact ALMA Core angular diameter Note: R Jeans ≈ 0.03 pc ACA

HII region molecular core Orion I Beuther et al. (2005) SMA

HII opaque core maximum ALMA resolution: HPBW = 0.012” (350 GHz/ν) Example: All HIIs in O9 stars usable up to 10 kpc with HII radius of 200 AU matching ALMA beam of 0.05” at 90 GHz

A primer for high-mass star formation IMF problem: OB stars born in clusters  clump fragmentation  core MF = stellar IMF? Radiation pressure problem: for M star > 8 M O t KH < t acc  reach ZAMS deeply embedded  radiation pressure halts accretion!? Lifetime problem: typical accretion rates in low-mass stars M O /yr  embedded phase of high-mass stars >10 6 yr  MS lifetime!?